Multi-layer piezoelectric actuators constituted from piezoelectric layers and internal electrodes stacked alternately one on another have been known as an example of the multi-layer piezoelectric element. The multi-layer piezoelectric actuators can be divided into two categories: fired-at-once type and stacked type that comprises piezoelectric porcelain and internal electrode sheet stacked alternately one on another. When the requirements to reduce the operating voltage and the manufacturing cost are taken into consideration, the multi-layer piezoelectric actuator of fired-at-once type has been recognized to be more advantageous for the reason of smaller layer thickness.
FIG. 7 shows a multi-layer piezoelectric actuator of the prior art. This multi-layer piezoelectric actuator comprises a stack 53 formed by stacking piezoelectric layers 51 and internal electrodes 52 one on another. Placed on both end faces of the stack in the direction of stacking are inactive layers 55. The internal electrodes 52 are formed so that one end thereof is exposed on the side face of the stack 53 on the right hand side in one layer and on the left hand side in the next layer, and an external electrode 70 is formed on the side face of the stack 53 where the end of the internal electrode 52 is exposed. The other end of the internal electrode 52 is covered by an insulating material 61 so as to be isolated from the external electrode 70.
The multi-layer piezoelectric actuator of fired-at-once type has been manufactured by stacking a predetermined number of green ceramic sheets, which are formed from a calcined powder of piezoelectric material and an organic binder, with an internal electrode paste made by mixing a silver-palladium powder and a binder being printed on the ceramic green sheets, thereby forming a green compact from the stack, and firing the green compact after removing the organic materials by heating to a predetermined temperature.    Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No. 9-270540